3rd Gen Something that bugs me in Emerald (spoilers)

In Emerald, The player has to meet up with Wallace in the Cave of Origins to discuss where Rayquaza could be. The player is given 3 locations to choose from, which is Cave of Origins, Mt Pyre, and Sky Pillar. The part that bugs me is that the player couldn't have known about Sky Pillar prior to the event, unless it was referenced somewhere else before? I know the man in Fortree City mentions seeing a green dragon, and the player's rival mentions seeing it heading towards Route 131, but I don't recall ever seeing a reference to Sky Pillar.

edit: nevermind, a sailor NPC in Lilycove City mentions Sky Pillar. Still weird though that that NPC isn't a required interaction beforehand.